With respect to a flow rate of hydrogen to be supplied to a fuel cell, there are many probabilities where a hydrogen stoichiometric ratio (an amount of hydrogen to be introduced/an amount of hydrogen consumed for electric power generation) is ensured to lie at a value greater than 1 (for instance, 1.5), with hydrogen resulting from non-use in reaction being recirculated for the purpose of improving a coefficient of utilization of hydrogen.
When in use of ejectors for such recirculation, although there is a case where a single ejector is suffice, another case exists where two ejectors are switched over and selected for use depending upon the flow rate. But, when using the two ejectors to be switched over, it is required to provide switch over mechanisms and back flow protection mechanisms.
On example where such two ejectors are provided with the use of the switch-over mechanisms and the back flow mechanisms is disclosed in Japanese patent Provisional Publication No. 2002-56870.